1. Field of the Invention
This invention relates to air conditioning systems employing refrigeration units and in particular to such a system having improved dehumidification capabilities. This system is particularly adaptable to heat pumps and refrigeration systems wherein latent head cooling is controlled by regulating the temperature of the indoor coil in communication with the air to be conditioned.
2. Prior Art
It has been recognized in many geographical areas that proper air conditioning systems should not only lower the temperature of the space being served when the temperature therein has exceeded a predetermined level but should also decrease the relative humidity of the space as a function of the air conditioning. During the typical air conditioning operation air from the enclosure to be conditioned is circulated over a heat exchanger. The exchanger absorbs heat from the air lowering its dry bulb temperature. If the temperature of the air is lowered beneath its dew point, then moisture from the air is condensed onto the heat exchanger surfaces and the actual amount of moisture contained in the air is reduced. Should the air to be cooled not be lowered beneath the dew point, then no water will be removed from the air and there will be no dehumidification effect. In fact it is possible to increase the relative humidity of air being conditioned since if moisture is not removed from the air then when the dry bulb temperature is decreased the capability of the air to absorb moisture is also decreased and the ratio between the actual moisture contained in the air and the amount of moisture that may be contained within the air is increased. Consequently, relative humidity can increase during the air conditioning process.
To provide for additional latent cooling it is necessary to lower the temperature of the heat exchanger such that the air passing through the heat exchanger will be lowered in temperature below the dew point and moisture will be removed therefrom. The conventional way of reducing the temperature of the heat exchanger has been by varying the flow of air over the heat exchanger surface. A reduction in flow rate allows the temperature of the coil to decrease and consequently additional moisture may be removed from the air. Typical of this type of air volume control for improved dehumidification is U.S. Pat. No. 4,003,729.
The described apparatus and method herein utilize another method of lowering the temperature of the coil through which the air is passed. The indoor coil or evaporator has multiple refrigerant flow circuits. When the unit is in the cooling mode of operation and additional dehumidification is desired, one or more of the circuits are isolated from the remainder of the coil such that all of the refrigerant flow is directed through the remaining circuits. The effect of additional refrigerant flow through the remaining circuits and the same volume of air flow being in contact with those circuits is to lower the temperature of that portion of the heat exchanger because of the lowering of the suction temperature through which refrigerant is flowing and consequently to increase the amount of moisture removed from the air. The dehumidified and cooled air passing thru that portion of the coil where there is refrigerant flow is then mixed with the unconditioned air passing through the remainder of the coil prior to delivery to the enclosure being conditioned.
The apparatus and method described herein further provide for controlling the humidity level by utilization of a humidistat in communication with the air of the enclosure to be conditioned. Upon the humidistat sensing a humidity level within a predetermined range a valve mechanism is regulated to limit the number of flow circuits available for the refrigerant.
Through experimentation it has been discovered that most humans are comfortable when the temperature humidity index is less than 70. Once the temperature humidity index level reaches 75 approximately half the population is uncomfortable and at a level of 80 most of the population is uncomfortable. The temperature humidity index level is determined by multiplying the sum of the wet bulb and dry bulb temperatures by a factor of 0.4 and adding 15. It is the purpose of the present invention to decrease the dry bulb temperature through the normal air conditioning process and to decrease the wet bulb temperature such that a combination of these two factors maintains the temperature humidity index level within the comfort range. The utilization of a solenoid valve to limit refrigerant flow through part of the indoor coil provides for an additional reduction in wet bulb temperature which will allow the air in the enclosure to be maintained closer to the comfortable regions. Since a thermostat senses only dry bulb temperature an additional device such as a humidistat is necessary to evaluate the moisture content of the air.